JohnKSa said:Slide velocity is affected by a number of variables, the primary ones being the weight of the recoiling mass (slide/barrel combination in the case of a typical locked breech semi-auto pistol) and the muzzle momentum of the load being shot. The recoil spring must have some effect since it exerts a force opposite the recoil momentum. Exactly how much effect it has depends on the design of the firearm the strength of the recoil spring, how much compression it's under when installed, etc.
Last week I finished up a Sig LE Classic P series armorers course. This was covered in quite a fair amount of detail. In fact, it is pretty much the basis of how and why the Sig P229 and heavier one-piece slide came into being. The old 228 and two piece (stamp sheet, breech block, and weld) slides were getting beaten to death when it started looking like Sig needed to field a .40 S&W, 10mm, and the other ctg in contention for the FBI trials. And curiously, it's why the recommended LE service life of the recoil springs are 3yrs/5,000 miles... er, rounds- to preserve the life and integrity of the frames.Slide velocity is affected by a number of variables, the primary ones being the weight of the recoiling mass (slide/barrel combination in the case of a typical locked breech semi-auto pistol) and the muzzle momentum of the load being shot. The recoil spring must have some effect since it exerts a force opposite the recoil momentum. Exactly how much effect it has depends on the design of the firearm the strength of the recoil spring, how much compression it's under when installed, etc.
John Bercowitz did a simplified assessment of the physics of a 1911's operation and determined that the recoil spring soaked up about 20% of the slide's remaining energy after the barrel/slide unlock.Yes, of course it has some effect, just like hitting a bug with my windshield has some effect in slowing down my car.
Run through Bercowitz' analysis. It's quite good. You'll see that the spring absorbs about 20% of the slide's remaining kinetic energy after the barrel unlocks. Since that's the portion of slide travel that extracts and ejects the cartridge, it is certainly applicable to this discussion.All I'm trying to say is that the forces involved with accelerating the slide before barrel unlock are so strong that the spring has little effect on it.
Recoil springs certainly do absorb kinetic energy. They absorb it and store it as potential energy when they are compressed and then convert it back to kinetic energy when they are allowed to decompress. That's pretty basic physics. Bercowitz' analysis makes this plain as well, and is fairly readable.The slide's kinetic energy has to go somewhere and springs don't use up kinetic energy,
One way to get rid of kinetic energy is to give it to the empty case, hence guns that throw empty cases into the next zip code.
JohnKSa said:Ok, here's an interesting exercise. I'd be interested to see if you get the same results I did.
From a number of sources (and my own calculations) it turns out that the slide velocity on a typical 1911 pistol is about 25fps.
I calculated the amount of force required to accelerate the slide/barrel combination to 25fps during the time the bullet is in the barrel (5 or 6 tenths of a millisecond). Interestingly enough, it comes out much lower (almost 2/3 lower) than the total force applied to the breechface based on the pressure & force relationship. That means that nearly 2/3 of the force applied to the breechface is NOT being used to accelerate the slide/barrel combination to 25fps. Said another way, you don't need nearly 3400 something lbs of force to get the slide moving that fast, only about 1400 something lbs of force is all you need. My best guess is that extra force applied (3400-1400lbs force) is used up extracting and ejecting the case.
That is exactly correct. I was thinking about it this morning and realized that I had calculated the average force and compared it to the peak force.I have a simpler explanation. The average pressure during bullet acceleration is much lower than the peak pressure.